A series of breakthroughs achieved in molecular biology has resulted in a wide variety of genomic techniques, providing a large number of disease-inducing genes to be separated and identified. In this context, molecular biological techniques have been introduced in diagnosis and examination in the medical field, not only enabling diagnosis, which could not be implemented in former years, to be successfully made but also considerably reducing the time period (in days) for an examination.
Such rapid progress has been made mainly under the favor of nucleic-acid amplification testing (NAT), especially, the polymerase chain reaction technique (PCR technique: Saiki et al., Science, 239, 487-491 (1988)). Since the PCR technique allows nucleic acids in a solution to be amplified sequence-specifically, for example, the existence of virus, only a trace amount of which is contained in serum, may be indirectly proved by amplifying and detecting the nucleic acids, which are genes of the virus.
Using the PCR technique, however, in routine examination made at clinical sites involves some problems. To address these problems, in particular, it is indicated that the nucleic acid extraction and purification processes is important in pre-processing (Ohshima et al., JJCLA, 22(2), 145-150 (1997)). These problems are induced by inhibitors, known as, for example, hemoglobin in blood and a surface active substance used in the extraction process, which could not be removed in the nucleic acid purification process. The extraction process requires a tedious operation necessary for the technique and a large amount of labor by experts. For this reason, this process disturbs the new introduction of genetic testing into hospital laboratory rooms and it is eagerly desired to automate this proceed.
Similarly, in institutions, where molecular biological researches are conducted, plasmid DNA is commonly used as a substance used for genetic recombination, it is also desired to automate the nucleic acid extraction and purification processes from the standpoint of laborsaving.
A known method for collecting nucleic acids from a biological sample containing nucleic acids in the highly-purified form without containing inhibitors includes the method, which collects the nucleic acids, in such a manner that a surface active substance is caused to act on the biological sample under the existence of protease, separating the nucleic acids, phenol (and chloroform) is mixed with it, aqueous phase-organic phase separation is applied in a centrifuge several times, and collecting the nucleic acids in the form of precipitate from the water phase sample by adding alcohol. However, such a problem has arisen that this method of preparation requires an organic solvent such as phenol, a poisonous substance, in the process or the centrifugation process, or the automation of loading/unloading vessels in the centrifuge and dispensing a centrifuged solution is very difficult.
U.S. Pat. No. 2,680,462 discloses that silica particles capable of binding to the nucleic acids under the presence of a chaotropic substance are used as a solid phase for binding nucleic acids. In the U.S. Pat. No. 2,680,462, the method which collects the nucleic acids in such a manner that a sample containing nucleic acids is added in a reaction vessel with a silica-particle suspension and a guanidine thiocyanate buffer solution as a chaotropic substance and mixed together, a complex composed of the nucleic acids bound to the silica particles is precipitated using a centrifuge, supernatant liquid was removed, a cleaning liquid is added to the remaining complex for cleaning, the re-precipitated complex is cleaned in a ethanol water solution and further cleaned with acetone, acetone is removed off from the complex, and finally a elution buffer is added to the complex, after dried, for eluting the nucleic acids.
In JP-A No. 250681/1995, the method for purifying a DNA extraction liquid using a cartridge vessel having a quadruple-structured filtering member, wherein a glass powder layer is inserted between two glass fiber filters and membrane filters, is disclosed. In JP-A No. 250681/1995, the sample to be purified is extracted in such a manner that a prepared DNA-containing culture is pre-processed and pipetted on a trap filter, and then an elution reagent is added on it to elute plasmid DNA from a cell. In the purification process, the sample to be purified and sodium iodide are added in the cartridge vessel and vacuum-depressurization or centrifugation is applied to the cartridge vessel to absorb the plasmid DNA to the glass powder layer. Next, a cleaning buffer solution is added in the cartridge vessel, vacuum-depressurization or centrifugation is applied for cleaning, and then an elution buffer is added in the cartridge vessel, vacuum-depressurization or centrifugation is applied again to elute the plasmid DNA.
Besides, in JP-A No. 266864/1999, a method and an instrument for purifying nucleic acids using a nucleic acid capturing tip, which has a silica-containing solid phase therein, is disclosed. In this method, the nucleic acid capturing tip is detachably attached to a movable nozzle for liquid suction/discharge, a mixture of a substance for accelerating binding of the nucleic acids to the solid phase, and a nucleic acid-containing sample is aspirated into the nucleic acid capturing tip attached to the movable nozzle for liquid suction/discharge from the given vessel, the liquid is discharged from the nucleic acid capturing tip after the nucleic acids are bound to the solid phase, then a cleaning liquid is aspirated and discharged to clean the inside of the nucleic acid capturing tip, and finally an eluent is aspirated in the cleaned nucleic acid capturing tip to discharge the eluent containing the nucleic acids eluted from the solid phase in the purified sample vessel.